Everyone knows about how birds are sensitive to gases and that coal miners would take canaries with them as early detectors of dangerous gases like carbon monoxide...

But luckily for the birdies, they eventually developed the canary resuscitator! If the canary stared to become ill, they could open up the oxygen to save the birb :3

https://gamefaqs.gamespot.com/a/user_image/1/3/8/AAPV5JAAEvAy.jpg